On a Thursday afternoon in St Petersburg, Florida, Beth Koehler crouches over a cairn terrier named Ginger, trimming intently as fur collects around her feet. On Koehler’s arm is a scratch – red, jagged and freshly acquired, though not in the way one might expect of a dog groomer.

“There was no way I could pin the head,” Koehler says, referring to the snake that was partly responsible. She had grabbed hold however she could, which made it “pissed”: “It decided to coil up and just throw itself at me.” Startled, Koehler had fallen backwards, cutting herself on a vine – an injury far preferable to the bite of a Burmese python.

“I have never been bit,” she proudly adds. “Peggy’s been bit once, but really, we’re very careful.”

Three days a week, Koehler runs Hair of the Dog with her partner of 31 years, Peggy van Gorder. The other four days the couple are usually out chasing pythons as members of Patric: the Python Action Team – Removing Invasive Constrictors, which is managed by the Florida fish and wildlife conservation commission (FWC).

Koehler and Van Gorder’s love affair with Burmese pythons began in 2016, when the FWC held its second python challenge. (The first was held in 2013; there have been none since.) A month-long public hunt held on a vast expanse of state forests and other government-owned land north of Everglades national park, the challenge was designed to cull numbers while also raising public awareness about a growing ecological problem.

The couple registered and were issued a permit to hunt in designated areas of south Florida. Then they attended a live-capture tutorial, also offered by the FWC. “They bring one in a bag and they drop it on the ground, and they say: ‘Catch it!’” says Van Gorder, adding that this is where they learned the safest way to grab a snake is by its head.

After 80 hours of trudging through cypress forests and freshwater marshland, Koehler and Van Gorder did not catch a single snake, but fellow participants removed 106 pythons. Those who had caught the most and also the longest pythons shared in over $16,000 of prizes.

“We usually achieve our goals,” Koehler says, still disappointed by their efforts in the challenge. Determined, they acquired another permit (no longer required for 22 FWC-managed areas as of 2017, when the commission declared open season on pythons) and kept looking for another two months, until they came across an eight-footer. “My heart stopped,” Van Gorder recalls, though now the size seems, to both of them, almost quaint.

Burmese pythons have no natural predators here. They do, however, have an uncanny ability to swallow things significantly larger than their own heads. Able to grow to more than 20ft in length, these stealthy invaders ambush their prey, squeeze until the prey stops breathing and then split their jaw apart to take the prey whole. They can inflict a nasty wound on humans – when Van Gorder was bitten, it took five months for one of the broken teeth to work its way out – but the chances of anything more serious happening are slim (though not impossible). Masters of camouflage, they can slide by an eagle-eyed biologist in just a few inches of water, and they can cover huge distances. One was recently discovered coiled up on a floating crab pot more than 15 miles out to sea.

But it’s not just the smaller, soft animals who have been attacked. In December 2016, a YouTube video showed a Burmese python in Big Cypress national preserve, next to the Everglades, strangling an alligator. This viral video led the executive director of the South Florida water management district, who was horrified by what he saw, to create the district’s own Python Elimination Program, in 2017. “He said he wanted to put 25 outdoorsmen with guns out in the field,” recalls Mike Kirkland, an invasive animal biologist who was charged with assembling the original team.

Damage done by the pythons to south Florida ecosystems has become so acute in recent years that the quest to stop has turned into a collective crusade. Wildlife biologists, government agencies, zoos and universities are deploying a full arsenal of responses, from telemetry tracking to early research into pheromone manipulation.

An American alligator in its natural habitat in the Florida Everglades. Burmese pythons have been know to prey on alligators in the area. Photograph: Charles Ommanney/Getty Images

In addition, the FWC and the South Florida water management district each created independent python removal squads in 2017 of hardy, civic-minded individuals who are skilled at capturing the non-native constrictors. These individuals must be over 18, and they must pass a stringent vetting process. Once licensed as professionals, they are charged with removing pythons from a patchwork quilt of district, state and federal lands that also, in the case of the Python Action Team, includes Everglades national park, which is off-limits to non-Patric hunters. The issue is also on the minds of ordinary citizens who haven’t been officially tasked with stalking the species. When I mentioned the pythons in passing to a well-known Florida author, he emailed back a photo of himself holding up one he’d recently shot. “Them damn pythons,” he wrote.

Koehler and Van Gorder applied to the FWC and were accepted on the second round. They found a hatchling their first night on the job. “Nobody’s doing this for the money,” Van Gorder says, though team members are paid for their time and effort. Instead, she sees it as an act of community service. A self-described “army brat”, she is not really from anywhere. But she feels like she finally has a home in Florida. Catching the pythons is a way of “protecting what I care about, the environment and my home,” she says.

Though they have lost track of exactly how many pythons they’ve caught in the last few years – about 70, perhaps – this June the women became responsible for bagging the 500th python for the Python Action Team. “Our biggest so far is 12 and a half [feet],” says Van Gorder. “A beefy guy,” adds Koehler.

Some of the couple’s customers have caught wind of what they get up to in the wilderness. “They’re like, ‘Whatever you do, just keep them from getting up here.’” As Koehler says this, a small papillon dog skitters across the waiting room floor. I can’t help but ask if they’ve ever considered the fact that a Burmese python would swallow all of their clients’ pets if given half a chance. Both women laugh as Van Gorder retrieves a dog collar. It is made from the skin of a python hatchling. She crafts these herself.

The safest way to capture a python is by its head. Photograph: Charles Ommanney/Getty Images

Tom Rahill meets me at a gas station on the outskirts of Miami, not far from the Everglades and Francis S Taylor wildlife management area, which is where he has agreed to take me on a “python survey”. Like Koehler and Van Gorder, Rahill is a member of the Python Action Team. He’s also founder of the Swamp Apes, a grassroots organization that has been approaching the python problem in a very different way – to help veterans address trauma.

In 2008, Rahill, who lives in Fort Lauderdale, decided that his life had become depressingly conventional. “My wife had moved to Arkansas [for an academic position], my kids are grown, I’m still doing IT after 30 years, and I’m in suburbia,” he says, letting out a pained howl. To reconnect with nature, he began volunteering for the National Park Service in the Everglades, clearing trails and capturing pythons as part of an early removal program. “I’d have a python on my arm at like 2 or 3 in the morning,” Rahill recalls. “It was like a revelation.”

Around the same time, he was thinking about two family members in the armed services who were “banged up emotionally”. And then it occurred to him that what he was doing in the Everglades might be of value to them, too: “What a perfect group of people to get out here and experience the ruggedness of this, honor on a mission.”

The “mission” being the trail clearing and Burmese pythons. Describing it as “wilderness therapy”, Rahill estimates he has taken out more than a hundred veterans over the past 10 years, and he says that the adrenaline of the hunt gives them an opportunity to work through PTSD – a claim that has the backing of psychologists at the University of South Florida. The Swamp Apes do not kill pythons because the last thing a veteran needs is further exposure to violence, Rahill says. Instead, they name many of the snakes they catch and deliver them live to an FWC facility roughly 40 miles north-east of the Everglades, where a coordinator can humanely euthanize them.

With his ponytail and unruly beard, Rahill looks like he spends a lot of time out in the marsh, and he does: at least three nights a week, often until sunrise. He spontaneously bursts into song about snakes, about his grandson, about rural decline in America.

As dusk turns to darkness, we swing off the paved road on to a dirt levee surrounded by vast expanses of saw grass. White mayflies cover the windshield, and invisible midges (appropriately named “no-see-ums”) begin to bite my eyelids. Outside is an eerie quiet, the faint smell of watery rot, an orange glow from the city refracted across the wetlands. Nighthawks swoop through the headlights, but we keep our eyes fixed on the dirt, watching to see if it moves.

After nearly three hours of driving without a single python sighting – “I caught three last night!” Rahill protests – he pulls up behind another truck. He hands me off to two comrades, Sgt Joe “Mojo” Detre and Sgt Maj Tom Aycock.

Detre rides in the flatbed with a spotlight while Aycock, born to be a drill instructor, steers along the levee. “My wife was like: ‘This is the craziest thing,’” he says. But Melanie Aycock soon demanded they take her out too, and she has since become an avid python tracker herself. Both are now also members of the FWC’s Python Action Team, and they usually spend Valentine’s Day hunting.

Melanie suffers from debilitating migraines, which causes depression. “So being able to get her out and into nature, and exposed,” he says, “it’s kind of the same concept as getting the veterans out here.”

After another few hours of driving, we have still seen no pythons. But Aycock and Detre are not particularly bothered; there’s always tomorrow, or next week. Before we part ways, Aycock says that he has something to show me.

We pull into a poorly lit section at the back of a casino and he and Detre lift a white box out of the truck. It looks like a beer cooler, except it’s padlocked and has air holes. Inside the box is a material bag, and inside the bag is a 9ft Burmese python that Aycock captured the night before and named Fred.

Liberated from the bag, the python writhes like an octopus tentacle. For a moment its tail coils around Detre’s calf. “See that? It’s trying to grab him,” Aycock says, launching into another story about the time a python coiled around his own leg, and then his arm, and then went for his neck, until he bodyslammed it.

Behind us, patrons trickle out into the parking lot. A woman, singing to herself, wanders past and climbs into a car, blithely unaware of what is unfolding right next to her.

There are many unknowns when it comes to Burmese pythons in south Florida. The earliest recorded sighting was on the edge of Everglades national park in 1979, but nobody knows for sure how one became many. A popular (but possibly apocryphal) theory is that hundreds of them escaped from a breeding facility flattened in 1992’s Hurricane Andrew. Another theory, more widely accepted, is that the blame rests largely with irresponsible pet owners.

According to federal importation data, more than 99,000 Burmese pythons, which are native to south-east Asia, were brought into the US between 1999 and 2006 alone. Due to Florida’s amenable climate, obliging private ownership laws, and lax biosecurity, some of those became pets. Four different biologists I spoke with say that owners may have set their pythons free either in or around the Everglades when their endearing 12in hatchlings grew to several feet long and became unmanageable. A list of reptile and amphibian imports into Florida since 1863 shows that “pet trade” is responsible for more than 85% of introductions into the Florida environment, most of them occurring during the past six decades. Recognizing the link, the FWC made it illegal to have Burmese pythons as pets in Florida in 2010.

Much of what is known about the python invasion is due to efforts by the Conservancy of Southwest Florida and its collaborators – what Ian Bartoszek, the conservancy’s research manager, calls “six years of hard work of staying on the tail of these animals”.

When I visit the conservancy, an environmental advocacy not-for-profit in Naples, I am ushered into a lab filled with snake skeletons and a giant screen showing a map of south-west Florida covered in dots, each one representing a python that is currently being tracked. A freeze-dried constrictor is coiled up in the corner, but the star attraction is 16ft and 160lb of grossly intimidating girth draped across a dissection table.

“You should have seen us trying to pull this thing out of the freezer yesterday,” says Bartoszek, who is 42 but as passionate as a teenager at his first science fair.

In April 2015, Bartoszek and other conservancy biologists, along with land managers from Collier-Seminole state park, came across a female with an unusually distended middle. After moving the python, it started to regurgitate a white-tailed deer. The deer – a fawn – turned out to be 111% of the python’s own body weight, and it would have been even more had part of it not been already digested.

If left unchecked, the impact of such gorging will be silence. Native mammals are already being overwhelmed, either eaten or (like the Florida panther, which hunts deer) outcompeted for food. Pythons have been found to feed on at least 43 species of bird, too, including the magnificent frigatebird, which is an alarming achievement. (“It soars!” Bartoszek says.) What will remain – what already remains, in some areas – is a landscape empty of virtually every animal except fish, rats, a few amphibians and more snakes.

While Bartoszek talks, his colleagues slice the python’s underbelly open from head to tail. Inside are 86 eggs, arranged like rows of hand grenades.

Within a 55 sq mile chunk of Collier county, the conservancy has removed enough pythons to outweigh a small aircraft. Bartoszek and his team have also weaponized male pythons out in the field. By implanting radio transmitters and then letting them play “hide and seek”, these males expose the location of breeding females.

But for Bartoszek, this is only the beginning, a kind of reconnaissance period. “What we’re after is understanding,” he says. “How many of them are making it to adulthood? What’s the sex ratio? How old are they when they start reproducing?”